Method and apparatus for tire uniformity measurement

ABSTRACT

There is provided a method and a apparatus for measuring tire uniformity. The apparatus comprises a spindle, a rotating drum, a sensor and a computing means. The method comprises the steps of mounting a tire on the spindle, pressing a circumferential surface of a rotating drum against the tread surface of the tire with a first pressing force, rotating the tire around rotational axis thereof, and computing the forces which the tire acts on first and second planes of the tire by the computing means while the tire is rotating. The first plane is perpendicular to the rotational axis and in one sidewall side of the tire. The second plane is perpendicular to the rotational axis and in the other sidewall side of the tire. The forces are computed based on values obtained by the sensor measuring forces transmitted to the spindle from the tire at first and second positions. The first and second positions have different distances from the tire in the rotational axis direction.

FIELD OF THE INVENTION

This invention relates to a method and an apparatus for tire uniformitymeasurement.

BACKGROUND OF THE INVENTION

Ideally, a tire is desirable to be a perfect circle, and interiorstiffness, dimensions and weight distribution and other features thereofshould be uniform around the circumference of the tire. However, theusual tire construction and manufacturing process make it difficult tomass produce such an ideal tire. That is, a certain amount ofnonuniformity in the stiffness, dimensions and weight distribution andother features occur in the produced tire. As a result, an excitingforce is produced in the tire while the vehicle is running. Theoscillations produced by this exciting force are transmitted to thevehicle chassis and cause a variety of vehicle oscillations and noisesincluding shaking, fluttering, sounds of the tire vibrations beingtransmitted inside the vehicle, and beat sounds.

One known method for evaluating nonuniformity of a tire is described inAutomobile Standards “Uniformity testing methods for automobile tires”(JASO C607). In this method, a rotating drum, which serves as asubstitute for the road surface, presses against a rotatably held tirewith a predetermined pressing force (several hundred kilograms), or thetire is pressed against the rotating drum with the predeterminedpressing force. The tire and the rotating drum are capable of rotatingaround their respective rotational axes, in such a way that when eitherone rotates, the other is also caused to rotate.

In this condition, the tire or the rotating drum is rotatably driven sothat the tire rotates at 60 [rpm]. As the tire rotates, the excitingforce produced by nonuniformity of the tire occurs. This exciting forceis measured by one or more means for measuring force (such as a loadcell) mounted on a bearing which rotatably supports the tire or therotating drum, or mounted on a member attached to this bearing. From themeasured value, an index that serves to evaluate the nonuniformity ofthe tire is computed. This measurement is called as a uniformitymeasurement. The index obtained by means of this uniformity measurementis computed by modeling the tire as a disc (this model will be called asa “disc model” hereinafter) and assuming that the force is concentratedat the center of that disc.

Next, tires on which measurements were performed are classified intothose for which the nonuniformity obtained from the index is withintolerable limits and those for which it is not. To the extent possible,tires for which the nonuniformity is outside of the tolerable limits aresubjected to processing to decrease the nonuniformity. Tires that havebeen processed are then subjected to uniformity measurement again; thosefor which the nonuniformity is within tolerable limits are separatedfrom those for which it is not.

Through the procedure described above, only tires judged to have“nonuniformity within tolerable limits” are selected and shipped tocustomers (or sent to the next step in the tire evaluation procedure).

Recently, a problem has occurred in that even when nonuniformity asmeasured by the uniformity measurement method described above is judgedto be within tolerable limits, particularly in high speed vehicleoperation, an exciting force from a tire is sometimes applied to thevehicle shaft, causing vehicle oscillations and noise inside thevehicle. The cause of these oscillations and noise is considered to benonuniformity that could not be evaluated from the result of measurementby the conventional uniformity measurement method. Therefore, anonuniformity measurement method that makes it possible to evaluate thenonuniformity that is causing these phenomena has been desired.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a tire uniformitymeasurement method for detecting the nonuniformity of a tire, which iscapable of evaluating a tire whether the tire causes above-describedphenomena.

An aspect of the present invention relates to detect the fluctuation inthe exciting force produced by nonuniformity in a tire lateral direction(i.e., a direction of the tire rotational axis). That is, when excitingforces are produced by nonuniformities of opposite phases on both sidesof the tire in the lateral direction, these exciting forces of oppositephase canceled each other out during the detection if the measurement isbased on the “disc model”. These exciting forces of opposite phase maynot be cancelled and may be applied to the vehicle shaft. Thus,according to an embodiment of the invention, it becomes possible todetect an index which can pick up tires which may produce vibrations ofthe vehicle chassis and noise inside the vehicle, even if excitingforces of opposite phases occur on the two sides of the tire in thelateral direction.

According to an embodiment of the invention, there is provided a tireuniformity measurement method which comprises the steps of mounting atire on a spindle of a uniformity measurement apparatus, pressing acircumferential surface of a rotating drum against the tread surface ofthe tire with a first pressing force, rotating the tire aroundrotational axis thereof, and computing the forces which the tire acts onfirst and second planes of the tire while the tire is rotating. Thefirst plane is perpendicular to the rotational axis and in one sidewallside of the tire. The second plane is perpendicular to the rotationalaxis and in the other sidewall side of the tire. The forces are computedbased on a measured values obtained by measuring forces transmitted tothe spindle from the tire at first and second positions. The first andsecond positions have different distances from the tire in therotational axis direction.

Optionally, the first plane includes the one sidewall of the tire andthe second plane includes the other sidewall of the tire.

Optionally, the first pressing force is determined by dividing theweight of a vehicle on which the tire is mounted by the number of tiresmounted on the vehicle.

Optionally, the method measures forces by which the tire acts on thefirst and second planes of the tire while the tire is rotating and thecircumferential surface of the rotating drum is pressed against thetread surface of the tire with a second pressing force. The secondpressing force produces a friction force between the rotating drum andthe tire. The friction force is so large as enough to prevent freerotation of the rotating drum and is smaller than the measurement errorof the forces measured at the first and second positions.

Optionally, one of the forces which the tire acts on first and secondplanes of the tire exceeds a predetermined value when thecircumferential surface of the rotating drum is pressed against thetread surface of the tire with the first pressing force, the pressingforce with which the circumferential surface of the rotating drum ispressed against the tread surface of the tire is changed into the secondpressing force, and the forces which the tire acts on the first andsecond planes of the tire are measured.

In one embodiment of the present invention, a calibration is performedon uniformity measurement apparatus using the result of measurement ofthe forces at the first and second positions when a predetermined weightis attached at a predetermined position on the first plane of a balancedtire and when the predetermined weight is attached at a predeterminedposition on the second plane of a balanced tire.

The other object of the invention is to provide a tire uniformitymeasurement apparatus for detecting the nonuniformity of a tire, whichis capable of evaluating a tire whether the tire causes above-describedphenomena.

According to an embodiment of the invention, there is also provided atire uniformity measurement apparatus, comprising a spindle for rotatinga tire around the rotational axis thereof, a rotating drum pressedagainst the tread of the tire with a first pressing force, a sensor formeasuring force transmitted from the tire to the spindle, and acomputing means for computing the forces by which the tire acts on firstand second plane. The rotating drum is adapted to rotate around therotational axis thereof as the tire rotates. The sensor measures theforce transmitted from the tire to the spindle at a first position and asecond position. The first and second positions have different distancesfrom the tire in the rotational axis direction. The force computed bythe computing means on the first plane is perpendicular to therotational axis and in one sidewall side of the tire. The force computedby the computing means on the second plane is perpendicular to therotational axis and in the second sidewall side of the tire. Thecomputing is performed based on the results of measurements by thesensor.

Optionally, the computing means computes the components of the forcesacting on first and second planes, respectively. Each of the componentsis in the direction tangential to both of the tire and the rotatingdrum.

Optionally, the first plane includes the one sidewall of the tire andthe second plane includes the other sidewall of the tire.

Optionally, the first pressing force is determined by dividing theweight of a vehicle on which the tire is mounted by the number of tiresmounted on the vehicle.

Optionally, apparatus measures forces by which the tire acts on thefirst and second planes of the tire while the tire is rotating and thecircumferential surface of the rotating drum is pressed against thetread surface of the tire with a second pressing force. The secondpressing force produces a friction force between the rotating drum andthe tire. The friction force is so large as enough to prevent freerotation of the rotating drum and is smaller than the measurement errorof the forces measured at the first and second positions.

Optionally, one of the forces which the tire acts on first and secondplanes of the tire exceeds a predetermined value when thecircumferential surface of the rotating drum is pressed against thetread surface of the tire with a first pressing force, the pressingforce with which the circumferential surface of a rotating drum ispressed against the tread surface of the tire is changed into the secondpressing force, and the forces which the tire acts on the first andsecond planes of the tire are measured.

In one embodiment of the present invention, the apparatus furthercomprises a tire cutting means for cutting the tire so that theamplitude of fluctuation of the force by which the tire acts on thefirst plane and the amplitude of fluctuation of the force by which thetire acts on the second plane are decreased. The forces are measuredwhen the rotating drum is pressed against the tread of the tire with thefirst pressing force.

In one embodiment of the present invention, the apparatus furthercomprises a tire cutting means for cutting the tire so that theamplitude of fluctuation of the force by which the tire acts on thefirst plane and the amplitude of fluctuation of the force by which thetire acts on the second plane are decreased. The forces are measuredwhen the rotating drum is pressed against the tread of the tire with thesecond pressing force.

In one embodiment of the present invention, the apparatus furthercomprises a marking means for marking the position at which the tireshould be cut and the amount by which it should be cut so that theamplitude of fluctuation of the force by which the tire acts on thefirst plane and the amplitude of fluctuation of the force by which thetire acts on the second plane will be decreased. The forces are measuredwhen the rotating drum is pressed against the tread of the tire with thefirst pressing force.

In one embodiment of the present invention, the apparatus furthercomprises a marking means for marking the position at which the tireshould be cut and the amount by which it should be cut so that theamplitude of fluctuation of the force by which the tire acts on thefirst plane and the amplitude of fluctuation of the force by which thetire acts on the second plane will be decreased. The forces are measuredwhen the rotating drum is pressed against the tread of the tire with thesecond pressing force.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be understood and appreciated from thefollowing detailed description, taken in conjunction with the drawingsin which:

FIG. 1 shows a front view of a high speed tire uniformity measurementapparatus according to an embodiment of this invention;

FIG. 2 is a detailed block diagram of the control section 400 in FIG. 1;

FIG. 3 is a time chart showing the tire dynamic balance and uniformitymeasurement method using the measurement apparatus 1, according to theembodiment shown in FIG. 1; and

FIG. 4 is a time chart showing the tire dynamic balance and uniformitymeasurement method using the measurement apparatus 1, according to themodified embodiment of this invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, embodiments of the invention will be described.

First Embodiment

FIG. 1 shows a front view of a high-speed tire uniformity measurementapparatus which is an embodiment of this invention. The measurementapparatus 1 which is an embodiment of this invention measures thehigh-speed uniformity of the tire, the uniformity according to JAS 0 C607 standard, and the tire dynamic balance. In addition, it includes amarking apparatus which can mark the tire for use in removing tireunbalance. Dynamic balance is measured by rotating the tire in freerotation and measuring the centrifugal force that arises at that time.In this invention, the tire is rotated together with a rotating drum,with the rotating drum pressed against the tire tread surface. Thepressing force which presses the tire against the rotating drum is setsmall, to 50 to 80 [kgf]. Among the forces acting on the tire,fluctuation of a component perpendicular to the tire rotational axis andthe direction in which the tire is pressed, is measured. Thesefluctuation does not include the pressing force which presses the tire.In addition, since the pressing force which presses the tire is set tobe low, the fluctuation amplitude can be regarded as nearly equivalentto the component in the radial direction of the tire of the centrifugalforce received by the tire rotational shaft when the tire rotatesfreely. Accordingly, the index obtained by using this fluctuation isnearly equivalent to the dynamic balance of the tire computed from theradial component, in the radial direction of the tire, of thecentrifugal force received by the tire rotational shaft when the tire isrotated in free rotation.

The measurement apparatus 1 has a spindle section 200 which rotatablyholds a wheeled tire W. The spindle section 200 comprises a spindle 201to which the tire is attached and which rotates together with the tire,a spindle housing 202 which rotatably supports the spindle 201 throughthe bearing 204, and a top adapter 203 which fixes the tire on thespindle 201.

A through-hole 202 a is formed in the spindle housing 202 in thevertical direction, and the spindle 201 is inserted into thisthrough-hole 202 a. The spindle 201 comprises a chuck section 201 a anda shaft section 201 b that extends downward from the chuck section 201a. The shaft section 201 a of the spindle 201 is inserted into andengaged with the through-hole 202 a in the spindle housing 202 via aplurality of bearings 204. Accordingly, the spindle 201 is rotatablysupported by the spindle housing 202.

The top adapter 203 has a shaft 203 a which extends vertically downward.This shaft 203 a can be inserted into a hole 201 c formed in the topsurface of the chuck section 201 a. The hole 203 c in a chuck section201 a is formed so as to be coaxial with the chuck section 201 a. Inaddition, the chuck section 201 a is provided with a lock mechanism thatlocks the shaft 203 a in a similar manner as described in the patentdisclosure 2003-4597A by the present applicant. The wheeled tire W isplaced on the top surface of the chuck section 201 a of the spindle 201so that the hub hole in the tire and the hole 201 c in the chuck section201 a are arranged coaxially. Then, the shaft 203 a of the top adapter203 is inserted into the hole 201 c so that the top adapter presses thewheel of the tire W toward the top surface of the chuck section 201 a.The tire W is then fixed to the spindle 201, so as to become integratedwith the spindle 201, by locking the shaft 203 a. At this time, the tireW is fixed in place so that the hub hole of the tire W and the spindle201 become coaxial, by using the mechanism described in patentpublication 2003-4597A. As a result, the tire W is able to rotate aroundits rotational axis. In addition, the rotational rate of the spindle 201and the phase of the spindle 201 can be detected by a rotary encoder 205attached to the spindle housing 202. The output from the rotary encoder205 is sent to a control section 400 of the measurement apparatus 1.

In this embodiment, the wheeled tire W is attached to the spindle,however, it is also possible for a wheelless tire to be retained betweenthe upper rim and the lower rim, and attached to the spindle as in theapparatus described in patent publication 2002-350293A.

The spindle 201 and the tire W attached to the spindle 201, arerotatably driven by a rotating drum section 300.

The rotating drum section 300 has the rotating drum 301. The rotatingdrum 301 is a cylindrical member which is capable of rotating around itsrotational axis. The rotational axis of the rotating drum 301 and therotational axis of the spindle 201 are substantially parallel. Inaddition, the rotating drum section 300 has a motor that rotationallydrives the rotating drum 301. That is, the rotational motion of therotational shaft of the motor 302 is transmitted to the rotational axisof the rotating drum 301 by a transmission system 303.

The transmission system 303 comprises a drive pulley 303 a, a drivenpulley 303 b and an endless belt 303 c. The drive pulley 303 a isattached to the rotational shaft of the motor 302 and the driven pulley303 b to the rotational shaft of the rotating drum 301, respectively.The endless belt 303 c is wound around the drive pulley 303 a and drivenpulley 303 b. The rotational motion of the motor 302 is transmitted tothe rotating drum 301 via this belt-pulley mechanism. That is, it ispossible to rotate the rotating drum 301 by driving the motor 302. Themotor 302 is a stepping motor, and its rotational rate can be controlledby the control section 400. Therefore, in the high speed uniformitymeasurement apparatus 1 of the embodiment, the rotating drum 301 can berotated at the desired rotational rate.

The rotating drum loading mechanism 304 is formed in the base section100. The cylindrical surface 301 a of the rotating drum 301 can move therotating drum 301, the motor 302 and the transmission system 303 in thehorizontal direction (the left-right direction in the Figure) such thatthey approach toward or away from the tread surface of the tire W.Further, by the rotating drum pressing mechanism 304, the cylindricalsurface 301 a of the rotating drum 301 can press tread surface of thetire W at a predetermined pressing force. T he rotating drum pressingmechanism 304 moves the motor 302 and the transmission system 303 in thehorizontal direction by a rack-pinion mechanism. The control section 400can control the positions of the rotating drum 301, the motor 302 andthe transmission system 303, and the magnitude of the pressing forcewhich presses the cylindrical surface 301 a of the rotating drum 301against the tread surface of the tire W, by controlling this rack-pinionmechanism. A load cell 304 a is mounted on the rack-pinion mechanism ofthe rotating drum pressing mechanism, and thereby the measurement of themagnitude of the pressing force by which the cylindrical surface 301 aof the rotating drum 301 presses the tread surface of the tire W can beperformed.

One side surface 202 a of the spindle housing 202 is opposite the rigidwall 102 of the base section 100. This side surface 202 a of the spindlehousing 202 is a flat surface which is parallel to the rotational axisof the spindle 201, and is perpendicular to the direction in which therotating drum 301 presses against the tire. In addition, this sidesurface 202 a and the rigid wall 102 are substantially parallel. Theupper side load cell 501 and the lower side load cell 502 are positionedin the gap G between the side surface 202 a and the rigid wall 102. Theload cells 501 and 502 are both members on a flat plate; both surfacesof the load cells are positioned so that they contact one side surface202 a of the spindle housing 202 and the rigid wall 102. The load cells501 and 502 are arranged in the axial direction of the spindle 201. Therigid wall 102 of the base section 100 is configured so that it isalmost neither displaced nor deformed at all. Therefore, the rigid wall102 provides an opposing force to the spindle housing 202, the opposingforce balancing with the force by which the rotating drum 301 pressesagainst the tire W. In addition, the load cells 501 and 502, which aregripped between the rigid wall 102 and the spindle housing 202, are ableto detect the force occurred by displacement of the spindle housing 202.The load cells 501 and 502 are able to detect pressing forces applied tothem in triaxial directions. That is, the load cells 501 and 502 areable to detect the pressing forces applied to them as 3-dimensionalvector quantities.

With the tire W set on the spindle 201, the cylindrical surface 301 a ofthe rotating drum 301 is pressed against the tread surface of the tire Wwith a predetermined pressing force, and the rotating drum 301 and thetire W are rotated together by driving the motor 302. At this time, thepressing force by which the rotating drum 301 presses the tire W and theexciting force arising from the nonuniformity of the tire W are appliedto the load cells 501 and 502. The outputs of the load cells 501 and 502are sent to the control section 400. The control section 400 processesthe load cell output results and computes the value of the tireuniformity index and the position of the tire to be cut and the amountof cutting needed to decrease the tire nonuniformity. Further, thecontrol section 400 controls the marking means 600 so as to mark thetire to indicate the tire cut position and cutting amount computedabove. A tire on which such a mark has been made is buff-processed by anappropriate tire cutting apparatus to decrease the tire nonuniformity.Instead of using the marking means 600, a cutting means such as acutting tool could be used in a configuration that makes it possible forthe measurement apparatus 1 to perform the buff alteration needed todecrease the nonuniformity.

The following explanation applies to the configuration of the controlsection 400. FIG. 2 shows a detailed block diagram of the controlsection 400 in FIG. 1. The control section 400 comprises a CPU 401, amemory 402, an I/O controller 403, a input means 404, a video controller405, a monitor 406, first through third filters 411, 421 and 431, andfirst through third A/D converters 412, 422 and 432.

The input means 404 is, for example, a keyboard. The operator of themeasurement apparatus 1 operates this input means 404 to direct themeasurement apparatus 1 to perform various measurements and calibration.The input means 404 is connected to the I/O controller 403; the CPU 401controls the I/O controller 403 to read out the input contents input bythe input means 404.

The CPU 401 controls the I/O controller 403 to perform variousmeasurements and calibration corresponding to the contents of theinstructions included in the contents of input by the input means 404. Amotor 302 (FIG. 1) which drives the rotating drum 301, a rotary encoder205 and a motor which drives the rack-pinion mechanism of the rotatingdrum pressing mechanism 304 are connected to the I/O controller 403. TheCPU 401 can rotate the rotating drum 301 so that the tire W rotates at adesirable rotation speed, and can move the rotating drum 301 toward oraway from the tire W, by controlling the I/O controller 403.

The output from the upper side load cell 501 is sent to the first filter411 (FIG. 2). The first filter 411 removes noise from the input signal.The signal from which noise has been removed is sent to the first A/Dconverter 412. The first A/D converter discretizes the input signal andsends it to the I/O controller 403.

Similarly, the output from the lower side load cell 502 (FIG. 1) ispassed through the second filter 421 (FIG. 2) where noise is removedfrom it; next, it is discretized in the second A/D converter 422 andthen sent to the I/O controller 403. The output from the load cell 304 a(FIG. 1) attached to the rack-pinion mechanism of the rotating drumpressing mechanism 304 (FIG. 1) is passed through the third filter 431(FIG. 2) where noise is removed from it, then it is discretized in thethird A/D converter 432, and finally sent to the I/O controller 403.

The CPU 401 controls the I/O controller 403. The discretized signalssent from the first, second and third A/D converters can be read out andstored in the memory 402 as digital data. Further, the CPU 401 processesthe digital data stored in the memory 402 and computes various measuredvalues. The CPU 401 controls the video controller 405 and can displayimage information related to the computed measured values (for example agraph showing fluctuations of the tire exciting force as a function oftire phase) on the monitor 406.

We now describe the method for measuring tire uniformity and dynamicbalance using the measurement apparatus 1 of this embodiment asdescribed above.

First, calibration is performed. The “calibration” referred to here isthe determination of the coefficient for computing the forces actuallyreceived by the load cells from the load cell output signals; anddetermination of the coefficient for computing the force acting on theplane including the upper sidewall of the tire in FIG. 1 (referred tobelow as the upper surface) and the force acting on the plane includingthe lower sidewall of the tire in FIG. 1 (referred to below as the lowersurface), respectively, from the forces received by the load cells. Itis sufficient for the calibration of the coefficients used to computethe forces actually received by the load cells from the load cell outputsignals to be performed periodically (for example once per week),therefore it is not necessary to perform these calibrations every time atire is measured. Additionally, it is sufficient to perform thecalibration to determine the coefficient used to compute the forcesoccurring at the upper and lower tire surfaces, respectively, from theforces received by the load cells once for each type of tire.

First, calibration to determine the coefficient used to obtain the forcereceived by the load cell 304 a from the output level of the load cell304 a of the rotating drum pressing mechanism 304 is performed. In thiscalibration, a known load is applied in the direction of the loadapplied by the rotating drum pressing mechanism 304, that is to say thedirection in which the rotating drum pressing mechanism 304 moves therotating drum 301 (the left-right direction in FIG. 1), and thecoefficient that will give the force received by the load cell 304 afrom the output level of the load cell 304 a of the rotating drumpressing mechanism 304 is determined from the output at that time. Inthis embodiment, the output O₁ of the load cell 304 a and the force F₁applied to the load cell 304 a satisfy the equation F₁=a₁×O₁+b₁. Thecoefficients a₁ and b₁ are computed from O₁ in the unloaded conditionand O₁ when a load of known magnitude is applied to the rotating drum.The computed a₁ and b₁ are stored in the memory 402.

Similarly, calibrations are performed to determine the coefficients usedto obtain the forces received by load cells from the outputs of loadcells, for the upper side load cell 501 and the lower side load cell502. In this case, a force of known magnitude is applied to the spindlehousing 202, and the outputs of the load cells 501 and 502 at that timeare used to determine the coefficient used to obtain the forces receivedby the load cells from the load cell output levels. Each of the upperside load cell 501 and the lower side load cell 502 measures forcecomponents in 3 mutually orthogonal directions (to be referred to belowas the x, y and z directions, respectively), therefore the calibrationsare performed for each component. In addition, as shown in FIG. 1, sincethe spindle housing 502 is a kind of cantilever beam wherein thepositions at which the load cells 501 and 502 are mounted are defined assupport points, the load on the spindle housing 202 is dividedlydistributed to the load cells 501 and 502.

Therefore, when a force Fx is applied to the spindle housing 202 in thex component direction, the relation given by the Equations (1) holdsamong the magnitude Fx₁ of the force in the x component directionreceived by the load cell 501, the x component output Ox₁ of the loadcell 501, the magnitude Fx₂ of the force in the x component directionreceived by the load cell 502 and the x component Ox₂ of the output ofthe load cell 502.Fx=Fx ₁ +Fx ₂Fx ₁ =ax ₁ ×Ox ₁ +bx _(q)   (1)Fx ₂ =ax ₂ Ox ₂ +bx ₂

The coefficients ax₁, bx₁, ax₂ and bx₂ are computed from Ox₁ and Ox₂ inthe unloaded condition and Ox₁ and Ox₂ when (at least 2 different) loadsof known magnitudes are applied to the spindle housing 202. In thisprocedure, the coefficients required to obtain the x components of theforces received by the load cells from the load cell output levels arecomputed for the upper side load cell 501 and the lower side load cell502. The coefficients required to obtain the y and z components of theforces received by the load cells from the load cell output levels arecomputed from the upper side load cell 501 and the lower side load cell502. The coefficients required to obtain the y and z components of theforces received by the load cells from the load cell output levels arecomputed by a similar procedure.

Next, calibration to determine the coefficients used to compute theforces acting on the top surface and bottom surface of the tire,respectively, from the forces received by the load cells is carried out.In this calibration, a tire which can be regarded as having neithernonuniformity nor unbalance (referred to below as the master tire), anda known weight, are used.

The weight of mass M is attached to the top surface of the master tireat a specified distance s from the rotational axis of the tire. At thistime, the top surface of the master tire is unbalanced by the weight,while the bottom surface remains without unbalance.

Next, the master tire is attached to the spindle 201. Next, the rotatingdrum pressing mechanism 304 is rotatably driven so that the rotatingdrum 301 presses on the master tire with a force of 50 to 80 [kgf]. Inother words, the rotating drum pressing mechanism 304 is driven so thatthe output of the load cell 304 a indicates 50 to 80 [kgf].

Next, the rotating drum 301 is rotatably driven by the motor 302. Atthis time, the master tire rotates together with the rotating drum. Whenit is detected from the output of the rotary encoder 205 that therotational rate of the master tire has reached a specified rotationalrate N, the CPU 401 (FIG. 2) controls the I/O interface 403 to acquirethe outputs of the load cells 501 and 502.

From the outputs of the load cells, the CPU 401 (FIG. 1) obtains thecomponents of the forces received by the load cells 501 and 502 in thetractive direction (the tangent direction of the rotating drum at theposition where the master tire is in contact with the rotating drum,that is to say the direction from the foreground toward the background,into the paper, in FIG. 1). The values that are obtained are TF₁(θ) andTF₂(θ). TF₁ is the value obtained from the output of the upper side loadcell 501, and TF₂ is the value obtained from the output of the lowerside load cell 502. θ is the phase of the spindle 201.

At this time, the force produced in the tire is the resultant of a forcethat can be regarded as practically the equivalent of the centrifugalforce produced by unbalance in the tire, and the force with which therotating drum 301 presses the tire. Since the force with which therotating drum 301 presses the tire is in a direction nearlyperpendicular to the tractive direction of the tire, the component inthe tractive direction of the centrifugal force produced at the topsurface of the master tire can be regarded as nearly equivalent to thecomponent in the tractive direction of the centrifugal force produced bythe tire unbalance. Therefore, the component in the tractive directionof the force produced at the top surface of the master tire isapproximately a sine wave with the absolute value of the signed maximaand minima being M×s×(2π×N)², and its phase depends on the position atwhich the weight is attached. This function is called Fm₁(θ). Among thecomponents in the front-rear direction of forces acting on the topsurface of the master tire, the proportion of force al received by thetop surface load cell 501 and the proportion (1−α₁) received by thebottom surface load cell 502 can be regarded as fixed, independent ofthe force acting on the top surface of the master tire. Thus, α₁ can becomputed by comparing Fm₁(θ), TF₁(θ) and TF₂(θ). Concretely,α₁=Fm₁(θ)/TF₁(θ).

Next, the rotation of the rotating drum 301 is stopped. Next, the weightis removed from the top surface of the master tire.

Next, the weight of mass M is attached to the bottom surface of themaster tire at a specified position a distance s from the rotationalaxis of the tire. At this time, the weight produces unbalance of thebottom surface of the master tire, while the top surface remains withoutunbalance.

Next, the rotating drum pressing mechanism 304 is driven to press therotating drum against the master tire with a force of 50 to 80 [kgf]. Inother words, the rotating drum pressing mechanism 304 is driven so thatthe output of the load cell 304 a indicates 50 to 80 [kgf].

Next, the rotating drum 301 is rotatably driven by the motor 302. Atthis time, the master tire rotates together with the rotating drum. Whenit is detected from the output of the rotary encoder 205 that therotational rate of the master tire has reached a specified rotationalrate N, the CPU 401 (FIG. 2) controls the I/O interface 403 to acquirethe outputs of the load cells 501 and 502.

From the outputs of the load cells, the CPU 401 (FIG. 1) obtains thecomponents of the forces received by the load cells 501 and 502 in thetractive direction. The values that are obtained are BF₁(θ) and BF₂ (θ).BF₁ is the value obtained from the output of the upper side load cell501, and BF₂ is the value obtained from the output of the lower sideload cell 502. θ is the phase of the spindle 201.

At this time, the force produced in the tire is the resultant of a forcethat can be regarded as practically the equivalent of the centrifugalforce produced by unbalance in the tire, and the force with which therotating drum 301presses the tire. Since the force with which therotating drum 301 presses the tire is in a direction nearlyperpendicular to the tractive direction of the tire, the component inthe tractive direction of the centrifugal force produced at the bottomsurface of the master tire can be regarded as nearly equivalent to thecomponent in the tractive direction of the centrifugal force produced bythe tire unbalance. Therefore, the component in the tractive directionof the force produced at the top surface of the master tire isapproximately a sine wave with the absolute value of the signed maximaand minima being M×s×(2π×N)², and its phase depends on the position atwhich the weight is attached. This function is called Fm₂(θ). Among thecomponents in the front-rear direction of forces acting on the topsurface of the master tire, the proportion of force α₂ received by thetop surface load cell 501 and the proportion (1−α₂) received by thebottom surface load cell 502 can be regarded as fixed, independent ofthe force acting on the top surface of the master tire. Consequently, α₂can be computed by comparing Fm₂(θ) and BF₁(θ), BF₂(θ). Accordingly,α₂=Fm₂(θ)/BF₁(θ).

The exciting force produced at the top surface of the tire and theexciting force produced at the bottom surface of the tire can becomputed from the outputs of the load cells 501 and 502 by using α₁ andα₂ determined above. That is, suppose that, in a given tire, TTW is thecomponent in the tractive direction of the exciting force which occursat the top surface and TBW is the tractive component of the excitingforce which occurs at the bottom surface. In addition, MF₁ is defined asthe component in the tractive directive direction of the force detectedby the top side load cell 501, and MF₂ is defined as the component inthe tractive direction of the force detected by the bottom side loadcell 502. At this time, relations such as those given in Equations 2among TTW, TBW, MF₁ and MF₂ are satisfied.MF ₁ =TTW×α ₁ +TBW×α ₂MF ₁ =TTW×(1−α₁)+TBW×(1−α₂)   (2)

It can be seen from Equations 2 that TTW and TBW can be computed fromEquations 3.TTW=((1−α₂)×MF ₁−α₂ ×MF ₂)/(α₁−α₂)TBW=((1−α₁)×MF ₁−α₁ ×MF ₂)/(α₂−α₁)   (3)

Using α1 and α2 obtained above, the components in the tractive directionof the exciting forces which occur at the top surface and bottomsurface, respectively, of the tire can be found from the components inthe tractive direction of the forces received by the load cells 501 and502.

Next, calibration is performed to determine the coefficients needed tofind the component in the radial direction (the direction from theposition where the master tire and the rotating drum are in contact,that is, the left-right direction in FIG. 1) of the resultant of theforce received at the top surface of the tire and the exciting forcethat occurs at the top surface of the tire, and the component in theradial direction of the resultant of the force received at the bottomsurface of the tire and the exciting force that occurs at the bottomsurface of the tire, from the components in the radial direction of theforces received by the load cells 501 and 502.

The weight of mass M is attached to the top surface of the tire at aspecified distance s from the rotational axis of the tire. At this time,unbalance due to the weight occurs at the top surface of the tire, whileat the same time the bottom surface remains free of unbalance.

Next, the rotating drum pressing mechanism 304 is driven so that therotating drum 301 presses the master tire with a force of about 50 to 80[kgf]. In other words, the rotating drum pressing mechanism 304 isdriven so that the load cell 304 a output indicates 50 to 80 [kgf]. Themagnitude of the force with which the rotating drum 301 presses themaster tire is fixed through this calibration. This magnitude is calledFD.

Next, the rotating drum 301 is rotatably driven by the motor 302. Atthis time, the master tire rotates together with the rotating drum. Whenit is detected from the output of the rotary encoder 205 that the mastertire rotational rate reaches the specified rotational rate N, the CPU401 (FIG. 2) controls the I/O interface 403 to acquire the outputs ofthe load cells 501 and 502.

The CPU 401 (FIG. 1) obtains the components in the radial direction ofthe forces received by the load cells 501 and 502 during one completerotation of the master tire. These values are called TF3 (θ) and TF4(θ). TF3 (θ) is the value obtained from the output of the top side loadcell 501, and TF4(θ) is the value obtained from the output of the bottomside load cell 502. θ is the phase of the spindle 201.

At this time, the force produced in the tire is the resultant of a forcethat can be regarded as practically the equivalent of the centrifugalforce produced by unbalance in the tire, and the force with which therotating drum 301 presses the tire. Therefore, the force in the radialdirection that acts on the top surface of the master tire isapproximated by a sine wave that has a maximum value of M×s×(2π×N)²+FD/2and a minimum value of M×s×(2π×N)²−FD/2. The phase is determined by theposition at which the weight is attached. This function is calledFm₃(θ). Among the components in the front-rear direction of forcesacting on the top surface of the master tire, the proportion of force β₁received by the top surface load cell 501 and the proportion (1−β₁)received by the bottom surface load cell 502 can be regarded as fixed,independent of the force acting on the top surface of the master tire.Consequently, β1 can be computed by comparing Fm₃(θ), TF₁(θ) and TF₂(θ).Concretely, β₁=Fm₃(θ)/TF₃(θ).

Next, the rotation of the rotating drum 301 is stopped. Next, the weightis removed from the top surface of the master tire.

Next, the weight of mass M is attached to the bottom surface of themaster tire at a specified position a distance s from the rotationalaxis of the tire. At this time, an unbalance due to the weight occurs inthe bottom surface of the master tire, while the top surface remainsfree of unbalance.

Next, the rotating drum pressing mechanism 304 is driven so that therotating drum 301 presses the master tire with force FD.

Next, the rotating drum 301 is rotatably driven by the motor 302. Atthis time, the master tire rotates together with the rotating drum. Whenit is detected from the output of the rotary encoder 205 that the mastertime rotational rate has reached the specified rotational rate of N, theCPU 401 (FIG. 2) controls the I/O interface 403 to acquire the outputsof the load cells 501 and 502.

The CPU 401 (FIG. 1) obtains the components in the radial direction ofthe forces received by the load cells 501 and 502 during one completerotation of the master tire. These values are called BF₃(θ) and BF₄(θ).BF₃(θ) is the value obtained from the output of the top side load cell501, and BF₄(θ) is the value obtained from the output of the bottom sideload cell 502. θ is the phase of the spindle 201.

At this time, the force produced in the tire is the resultant of a forcethat can be regarded as practically the equivalent of the centrifugalforce produced by unbalance in the tire, and the force with which therotating drum 301 presses the tire. Consequently, the force in theradial direction that acts on the top surface of the master tire isapproximated by a sine wave that has a maximum value of M×s×(2π×N)²+FD/2and a minimum value of M×s×(2π×N)²−FD/2. The phase is determined by theposition at which the weight is attached. This function is calledFm₄(θ). Among the components in the front-rear direction of forcesacting on the top surface of the master tire, the proportion of force β₂received by the top surface load cell 501 and the proportion (1−β₂)received by the bottom surface load cell 502 can be regarded as fixed,independent of the force acting on the top surface of the master tire.Accordingly, β₁ can be computed by comparing Fm₄(θ), BF₃(θ) and BF₄(θ).Concretely, β₂=Fm₄(θ)/BF₃(θ).

The resultant of the force applied to the top surface of the tire andthe exciting force produced at the top surface of the tire and theresultant of the force applied to the bottom surface of the tire and theexciting force produced at the bottom surface of the tire, can becomputed from the outputs of the load cells 501 and 502 by using β₁ andβ₂ determined above. That is to say, suppose that, in a given tire, RTWis the component in the radial direction of the resultant of the forceapplied to the top surface of the tire and the exciting force whichoccurs at the top surface, and RBW is the component in the radialdirection of the resultant of the force applied to the bottom surface ofthe tire and the exciting force which occurs at the bottom surface. Inaddition, let MF₃ be the component in the radial direction of the forcedetected by the top side load cell 501, and let MF₄ be the component inthe radial direction of the force detected by the bottom side load cell502. At this time, the relations given in Equations 4 among RTW, RBW,MF₃ and MF₄ are satisfied.MF ₃ =RTW×β ₁ +RBW×β ₂MF ₄ =RTW×(1−β₁)+RBW×(1−β₂)   (4)

From Equations 4, it is seen that RTW and RBW can be computed fromEquations 5.RTW=((1−β₂)×MF ₃−β₂ ×MF ₄)/(β₁−β₂)RBW=((1−β₁)×MF ₃″β₁×MF₄)/(β₂−β₁)   (5)

The dynamic balance and uniformity of the tire are measured using thecoefficients computed in the above calibration.

FIG. 3 is a time chart showing the measurement procedure of dynamicbalance and uniformity of a tire using the measurement apparatus 1. Inthis measurement procedure, for one tire the dynamic balancemeasurement, the high speed uniformity measurement and the uniformitymeasurement according to the JASO C 607 standard are performed in rapidsuccession. FIG. 3 is a time chart with elapsed time as the abscissa andtire rotational rate as the ordinate. The series of tests listed beloware carried out by the CPU 401, which executes programs stored in thememory 402 (FIG. 2) of the measurement apparatus 1.

First, the tire is attached to the spindle 201, and the tire is fixed tothe spindle 201 by the top adapter 203.

Next, the rotating drum 301 is pushed into contact with the tire. Next,the rotating drum 301 is pressed against the tire W with a force of 150[kgf] (FIG. 3: S101 (0 [sec])). This pressing force is determined bydividing the weight of a vehicle on which the tire W is mounted by thenumber of the tires. Generally, the pressing force is between 200 [kgf]and 1000 [kgf]. Next, in this condition the rotating drum 301 isrotatably driven (consequently the tire that is in contact with therotating drum 301 rotates together with the rotating drum 301); therotating drum 301 is accelerated until the tire rotational rate reaches1000 [rpm] (FIG. 3: S102 (0 to 2 [sec])). Next, the pressing force whichpresses the tire against the rotating drum 301 is set to 50 [kgf] (FIG.3: S103 (2 to 3 [sec])). This pressing force produces a friction forcebetween the rotating drum 301 and the tire W. The magnitude of thepressing force is determined such that the friction force is so large asenough to prevent free rotation of the rotating drum 301 and is smallerthan the measurement error of the forces measured by the load cells 501and 502. In general, the pressing force is between 50 [kgf] and 80[kgf].

In this embodiment of the invention, the time required from start of therotation of the rotating drum 301 until the rotational rate reaches 1000[rpm] is 2 seconds. In addition, after the tire rotational rate reaches1000 [rpm], the time required until the pressing force of the rotatingdrum 301 against the tire reaches 50 [kgf] is 1 second. Accordingly,until the start of measurement of the tire exciting force, the tirerotates 30 times or more while receiving a force of 50 to 150 [kgf] inthe horizontal direction. As a result, the tire is pushed downward, andthe tire rotational axis nearly coincides with the spindle rotationalaxis.

Next, the fluctuations of the load on the load cells 501 and 502 aredetected while the spindle 201 is rotating (FIG. 3: S104 (3 to 6[sec])). This detection is for the purpose of measuring the dynamicbalance of the tire. The load cells 501 and 502 are capable of measuringin 3 mutually orthogonal directions, but what is necessary to measurethe dynamical balance is the component in an arbitrary horizontaldirection. In this embodiment of the invention, the component of theload fluctuation in the tractive direction is detected in order toremove the effect of the load applied to the tire from the rotating drum301. Values nearly equivalent to the centrifugal forces produced by thedynamical unbalance of the top surface and the bottom surface of thetire, respectively, can be determined by substituting the detected loadfluctuation components into Equations 3. These dynamic unbalances areexpressed as functions of the tire phase θ. We let FT₁(θ) be thecentrifugal force acting on the top surface of the tire and FT₂(θ) bethe centrifugal force acting on the bottom surface of the tire. FT₁(θ)and FT₂(θ) are in units of [kgf].

The phase at which unbalance of the tire occurs and the magnitude of theunbalance are computed for the top surface and the bottom surface of thetire, respectively, from FT₁(θ) and FT₂(θ). That is to say, the phase atwhich unbalance occurs at the top surface of the tire is the phase atwhich FT₁(θ) becomes a maximum (this phase will be called θ_(max1)below); the phase at which unbalance occurs at the bottom surface of thetire is the phase at which FT₂(θ) is maximum (this phase is calledθ_(max2) below). Further, the magnitude UB₁ of the unbalance at the topsurface of the tire and the magnitude UB₂ at the bottom surface of thetire are computed from Equations 6. $\begin{matrix}{{{UB}_{1} = {{{FT}_{1}\left( \theta_{\max\quad 1} \right)} \times \frac{9.8}{\left( {6000 \times 2\pi} \right)^{2}}}}{{UB}_{2} = {{{FT}_{2}\left( \theta_{\max\quad 2} \right)} \times \frac{9.8}{\left( {6000 \times 2\pi} \right)^{2}}}}} & (6)\end{matrix}$

UB₁ and UB₂ are in units of [kg m]. Therefore, to remove the unbalanceat the top surface side, it is sufficient to remove the weight UB₁/s₁from the top surface of the tire at a position where the phase isθ_(max1), a distance s₁[m] from the rotational axis of the tire.Similarly, to remove the unbalance from the bottom surface of the tire,it is sufficient to remove the weight of material UB₂/s₂ from the bottomsurface of the tire, at a position where the phase is θ_(max2), adistance s2 from the rotational axis of the tire. Since these unbalancesare one of the causes of nonuniformity of the tire, removing theseunbalances will decrease the nonuniformity of the tire.

Next, a high speed uniformity test is performed with the rotating drum301 pressing the tire with a pressing force of 500 [kgf] (FIG. 3: S105[6 to 11] sec)). In this embodiment, the tire rotational rate is 1000[rpm] in the high speed uniformity test; this is intended to simulate avehicle with tires of diameter 600 to 700 mm running at 100 to 130[km/h]. Consequently, if a test is to be performed on a tire of largeror smaller diameter, the tire should be rotated at a differentrotational rate corresponding to a tire circumferential speed of 100 to140 [km/h]. The load fluctuations which the tire receives are detectedby the load cells 501 and 502. The RFV and TFV of the top surface of thetire, the RFV and TFV of the bottom surface of the tire, and the LFV ofthe entire tire are measured from these load fluctuations.

That is to say, the 3-dimensional vector loads received by the loadcells 501 and 502 are decomposed into components in the radialdirection, the lateral direction (the direction of the tire rotationalaxis) and the tractive direction by the CPU 401. These are expressed asfunctions of the tire phase θ. The forces received by the top side leadcell 501 (FIG. 1) in the radial direction, the horizontal direction andthe tractive direction, respectively, are taken to be TRF(θ), TLF(θ) andTTF(θ), respectively. In addition, the forces received by the bottomside load cell 502 in the radial direction, the lateral direction andthe tractive direction are denoted as BRF(θ), BLF(θ) and BTF(θ),respectively.

Next, RFV and TFV for the top surface of the tire, RFV and TFV for thebottom surface of the tire, and LFV for the whole tire are computed fromTRF(θ), TLF(θ), TTF(θ), BRF(θ), BLF(θ) and BTF(θ) using Equations 7.$\begin{matrix}\begin{matrix}{{RFV}\quad{at}\quad{the}\quad{top}\quad{surface}\text{:}} \\{{amplitude}\quad{of}\quad{fluctuation}\quad{of}{\quad\quad}\frac{{\left( {1 - \beta_{2}} \right) \times {{TRF}(\theta)}} - {\beta_{2}{{BRF}(\theta)}}}{\beta_{1} - \beta_{2}}}\end{matrix} & \quad \\\begin{matrix}{{TFV}\quad{at}\quad{the}\quad{top}\quad{surface}\text{:}} \\{{amplitude}\quad{of}\quad{fluctuation}\quad{of}\quad\frac{{\left( {1 - \alpha_{2}} \right) \times {{TTF}(\theta)}} - {\alpha_{2}{{BTF}(\theta)}}}{\alpha_{1} - \alpha_{2}}}\end{matrix} & \quad \\{\begin{matrix}{{RFV}\quad{at}\quad{the}\quad{bottom}\quad{surface}\text{:}} \\{{amplitude}\quad{of}\quad{fluctuation}\quad{of}\quad\frac{{\left( {1 - \beta_{2}} \right) \times {{TRF}(\theta)}} - {\beta_{2}{{BRF}(\theta)}}}{\beta_{1} - \beta_{2}}}\end{matrix}\quad} & (7) \\{\begin{matrix}{{TFV}\quad{at}\quad{the}\quad{bottom}\quad{surface}\text{:}} \\{{amplitude}\quad{of}\quad{fluctuation}\quad{of}\quad\frac{{\left( {1 - \alpha_{2}} \right) \times {{TTF}(\theta)}} - {\alpha_{2}{{BTF}(\theta)}}}{\alpha_{1} - \alpha_{2}}}\end{matrix}\quad{{{LFV}\quad{of}\quad{whole}\quad{tire}\text{:}\quad{amplitude}\quad{of}\quad{fluctuation}\quad{of}\quad{{TLF}(\theta)}} + {{BLF}(\theta)}}} & \quad\end{matrix}$

Next, a uniformity test is performed according to the JASO C607standard. That is to say, the rotating drum 301 is decelerated and thetire is rotated at 60 [rpm] (FIG. 3: S106 (11 to 14 [sec])). Then thefluctuation of the load received by the tire C is detected by the loadcells 501 and 502 (FIG. 3: S107 (14 to 17 [sec])). That is to say, theforces received by the top side load cell 501 (FIG. 1) in the radialdirection, the lateral direction and the tractive direction are denotedas TRF(θ), TLF(θ) and TTF(θ), respectively. Denoting the forces receivedby the bottom side load cell 502 in the radial direction, the lateraldirection and the tractive direction as BRF(θ), BLF(θ) and BTF(θ),respectively, RFV, LFV and TFV of the tire can be computed usingEquations 8.RFV: amplitude of fluctuation of TRF(θ)+BRF(θ)   [Equation 8]LFV: amplitude of fluctuation of TLF(θ)+BLF(θ)TFV: amplitude of fluctuation of TTF(θ)+BTF(θ)

Next, rotation of the tire and the rotating drum 301 is temporarilystopped, the rotation direction of the tire and the rotating drum 301 isinverted and the tire is rotated at 60 [rpm] (FIG. 3: S108 (17 to 18[sec])). Next, warm-up operation is performed (FIG. 7: S109 (18 to 20[sec])). Next, the fluctuation of the load received by the tire isdetected by the load cells 501 and 502 (FIG. 3: S110 (20 to 23 [sec])),and the uniformity is calculated based on the detected load fluctuationsusing Equations 8. Next, the tire and the rotating drum 301 aredecelerated (FIG. 3: S111 (23 to 24 [sec])), and rotation is stopped(FIG. 3: S112 (24 [sec])).

After measurement of the tire by the procedure described above iscompleted, the tire is removed from the measurement apparatus 1 andbuff—altered by the cutting apparatus to remove the unbalance componentsfrom the top surface and bottom surface of the tire.

As described above, based on this embodiment, by measuring theuniformity of the tire it is possible to distinguish a tire that haslarge nonuniformity of the top surface and/or the bottom surface. Inaddition, according to this embodiment, it is possible to remove dynamicunbalance that occurs at the top surface and/or bottom surface of thetire. Accordingly, among tire nonuniformities, it is possible to removeelements caused by dynamic unbalance, that is to say it is possible todecrease the tire nonuniformity. The present embodiment is configured sothat the resultant of the force received by the tire at its top surfaceand the exciting force that occurs at the top surface of the tire, andthe resultant of the force received by the tire at its bottom surfaceand the exciting force that occurs at the bottom surface of the tire,are determined from the forces received by 2 load cells, but based on asimilar principle, it is possible to have a configuration in which theforces received by the tire at each of its surfaces and the excitingforces which occur at each surface of the tire are calculated from theoutputs of a larger number of load cells.

In the embodiment described above, the configuration is such that theuniformity test according to the JASO C607 standard, the high speeduniformity test and the dynamic balance test are performed insuccession, but this invention is not limited to the configurationdescribed above. For example, it is possible for a testing apparatusaccording to this invention to be configured so that it normallyperforms only the uniformity test, and only when a nonuniformity of aspecified threshold value or greater is detected is a dynamic balancetest performed. Such an embodiment is described below.

Second Embodiment

FIG. 4 is a time chart showing the measurement procedure for measuringthe dynamic balance and uniformity of a tire using the measurementapparatus 1 in the second embodiment. In this embodiment, a high speeduniformity test and a uniformity test according to the JASO C607standard are performed on one tire. After the high speed uniformitymeasurement, depending on the result a dynamic balance test isperformed. Similarly to FIG. 3, FIG. 4 is a time chart having elapsedtime as the abscissa and tire rotational rate as the ordinate. Theseries of tests described below are carried out by execution of programsstored in the memory (FIG. 2) of the measurement apparatus 1 by the CPU401. In addition, before the measurements, calibrations similar to thosein the first embodiment are performed.

First, the tire is attached to the spindle 301, and the tire is fixed tothe spindle 201 by the top adapter 203.

Next, the tire is pushed into contact with the rotating drum 301. Next,the rotating drum 301 is pressed against the tire with a force of 150[kgf]. Next, in this condition the rotating drum 301 is rotated(consequently the tire in contact with the rotating drum 301 rotatestogether with the rotating drum 301). The rotating drum 301 isaccelerated until the tire rotational rate reaches 1000 [rpm] (FIG. 4:S202 (0 to 2 [sec])) Next, the pressing force with which the rotatingdrum 301 presses against the tire is set to 500 [kgf] (FIG. 4: S203 (2to 4 [sec])).

In this embodiment of this invention, the time required from the startof rotation of the rotating drum 301 until the tire rotational ratereaches 1000 [rpm] is 2 seconds. The additional time required, after thetire rotational rate reaches 1000 [rpm] until the pressing force bywhich the rotating drum 301 is pressed against the tire reaches 500[kgf], is 2 seconds. Consequently, until measurement of the excitingforce on the tire starts, the tire rotates 30 times or more whilereceiving a force of 50 to 500 [kgf] in the horizontal direction. As aresult, the tire is pushed downward, and the rotational axis of the tireand the rotational axis of the spindle 201 nearly coincide.

Next, the fluctuation of the load on the load cells 501 and 502 isdetected while the spindle 201 is rotating (FIG. 4: S204 (4 to 8[sec])). This detection is for the purpose of measuring the high speeduniformity of the tire. In this embodiment, also, the tire rotationalrate in the high speed uniformity test is set at 1000 [rpm] to simulatea vehicle with wheels of diameter 600 to 700 mm running at a speed of110 to 130 [km/h], In a test of tires of larger or smaller diameter, thetire would be rotated at a different rotational rate so that thecircumferential speed comes to 100 to 140 [rpm]. Then the fluctuation ofthe load received by the tire is detected by the load cells 501 and 502.The RFV and TFV of the top surface of the tire, the RFV and TFV of thebottom surface of the tire, and the LFV of the entire tire are measuredfrom these load fluctuations. The measurement method is similar to thatfor the first embodiment of this invention, so an explanation of it isomitted here.

Next, judgments are made as to whether or not the RFV values at the topsurface and the bottom surface of the tire exceed specified standardvalues (for example RFV=10 [kgf m], TFV=8 [kgf m]) (FIG. 4: S204 a (8[sec])) . If the RFV at either the top surface or bottom surface of thetire exceeds the standard value, next the dynamic balance and theuniformity according to the JASO C607 standard are measured. In thiscase, the tire rotational rate varies according to the dotted lines inFIG. 4.

Next, the pressing force with which the rotating drum 301 pressesagainst the tire is set to 50 [kgf], and the dynamic balance of the tireis measured (FIG. 4: S214 (8 to 11 [sec])) The method of measuring thedynamic balance is similar to that in the first embodiment, so anexplanation of it is omitted here.

Next, a uniformity test according to JASO C607 is performed. That is tosay, the rotating drum 301 is decelerated so as to rotate the tire at 60[rpm] and the pressing force with which the rotating drum 301 pressesagainst the tire is set to 500 [kgf] (FIG. 4: S215 (11 to 13 [sec])).Then the fluctuation of the load received by the tire C is detected bythe load cells 501 and 502 (FIG. 43: S216 (13 to 17 [sec])). The methodof measuring the uniformity from the load fluctuations is similar tothat in the first embodiment, so an explanation of it is omitted here.

Next, rotation of the tire and the rotating drum 301 is temporarilystopped, the direction of rotation of the tire and the rotating drum 301is reversed, and the tire is rotated at 60 [rpm] (FIG. 4: S217 (17 to 18[sec])). Next, warm-up operation is performed (FIG. 4: S218 (18 to 20[sec])). Next, the fluctuations of the load received by the tire aredetected by the load cells 501 and 502 (FIG. 4: S219 (20 to 23 [sec])),and the uniformity is calculated based on the detected loadfluctuations. Next, the tire and the rotating drum 301 are decelerated(FIG. 4: S220 (23 to 24 [sec]), and the rotation is stopped (FIG. 4:S221 (24 [sec])).

After measurement of the tire according to the procedure described abovehas been completed, the tire is removed from the measurement apparatus1, and buff-alteration is performed by a cutting apparatus to removeunbalance from the top surface and/or the bottom surface of the tire.

Meanwhile, if the RFV values at both the top surface and the bottomsurface of the tire are less than a standard value in S204 a, next theuniformity measurement according to the JASO C607 standard is performed.In this case, the rotational rate of the tire varies according to thesolid line in FIG. 4.

The rotating drum 301 is decelerated, and the tire is rotated at 60[rpm] (FIG. 4: S205 (9 to 11 [sec])). Then the fluctuation of the loadsreceived by the tire C is detected by the load cells 501 and 502 (FIG.4: S206 (11 to 14 [sec])). The uniformity measurement method from theload fluctuations is similar to that used in the first embodiment, so anexplanation of it is omitted here.

Next, rotation of the tire and the rotating drum 301 is temporarilystopped, the rotational direction of the tire and the rotating drum 301is reversed, and the tire is rotated at 60 [rpm] (FIG. 4: S207 (14 to 15[sec])). Next, warm-up operation is performed (FIG. 4: S208 (15 to 17[sec])). Next, the fluctuations of the load received by the tire aredetected by the load cells 501 and 502 (FIG. 4: S209 (17 to 20 [sec])),and the uniformity is calculated based on the detected loadfluctuations. Next, the tire and the rotating drum 301 are decelerated(FIG. 4: S210 (20 to 21 [sec]), and the rotation is stopped (FIG. 4:S211 (21 [sec])).

As described above, according to this embodiment, during the uniformitytest it is possible to measure a value that can be regarded asequivalent to the dynamic unbalance by decreasing the pressing force bywhich the rotating drum 301 presses against the tire to 50 to 80 [kgf],so that when dynamic balance measurement is necessary, the dynamicbalance test can be started immediately without stopping rotation of thetire.

1. A tire uniformity measurement method, comprising the steps of:mounting a tire on a spindle of a uniformity measurement apparatus;pressing a circumferential surface of a rotating drum against the treadsurface of the tire with a first pressing force; rotating the tirearound rotational axis thereof; and computing the forces which the tireacts on first and second planes of the tire while the tire is rotating,the first plane being perpendicular to the rotational axis and in onesidewall side of the tire, the second plane being perpendicular to therotational axis and in the other sidewall side of the tire, the forcesbeing computed based on a measured values obtained by measuring forcestransmitted to the spindle from the tire at first and second positions,the first and second positions having different distances from the tirein the rotational axis direction.
 2. A method according to claim 1,wherein said method computes the components of the forces acting onfirst and second planes, respectively, each of the components being inthe direction tangential to both of the tire and the rotating drum.
 3. Amethod according to claim 1, wherein the first plane includes the onesidewall of the tire and the second plane includes the other sidewall ofthe tire.
 4. A method according to any of claims 1-3, wherein the firstpressing force is determined by dividing the weight of a vehicle onwhich the tire is mounted by the number of tires mounted on the vehicle.5. A method according to claim 4, wherein said method measures forces bywhich the tire acts on the first and second planes of the tire while thetire is rotating and the circumferential surface of the rotating drum ispressed against the tread surface of the tire with a second pressingforce, the second pressing force producing a friction force between therotating drum and the tire, the friction force being so large as enoughto prevent free rotation of the rotating drum and is smaller than themeasurement error of the forces measured at the first and secondpositions.
 6. A method according to claim 5, wherein one of the forceswhich the tire acts on first and second planes of the tire exceeds apredetermined value when the circumferential surface of the rotatingdrum is pressed against the tread surface of the tire with the firstpressing force, the pressing force with which the circumferentialsurface of the rotating drum is pressed against the tread surface of thetire is changed into the second pressing force, and the forces which thetire acts on the first and second planes of the tire are measured.
 7. Amethod according to any of claim 1-3, wherein a calibration is performedon uniformity measurement apparatus using the result of measurement ofthe forces at the first and second positions when a predetermined weightis attached at a predetermined position on the first plane of a balancedtire and when the predetermined weight is attached at a predeterminedposition on the second plane of a balanced tire.
 8. A tire uniformitymeasurement apparatus, comprising: a spindle for rotating a tire aroundthe rotational axis thereof; a rotating drum pressed against the treadof the tire with a first pressing force, the rotating drum being adaptedto rotate around the rotational axis thereof as the tire rotates; asensor for measuring force transmitted from the tire to said spindle,the force being measured at a first position and a second position, thefirst and second positions having different distances from the tire inthe rotational axis direction; and a computing means for computing theforces by which the tire acts on first and second plane, the force onthe first plane being perpendicular to the rotational axis and in onesidewall side of the tire, the force on the second plane beingperpendicular to the rotational axis and in the second sidewall side ofthe tire, the computing being performed based on the results ofmeasurements by said sensor.
 9. An apparatus according to claim 8,wherein said computing means computes the components of the forcesacting on first and second planes, respectively, each of the componentsbeing in the direction tangential to both of the tire and the rotatingdrum.
 10. An apparatus according to claim 8, wherein the first planeincludes the one sidewall of the tire and the second plane includes theother sidewall of the tire.
 11. An apparatus according to claim 8,wherein the first pressing force is determined by dividing the weight ofa vehicle on which the tire is mounted by the number of tires mounted onthe vehicle.
 12. An apparatus according to any of claims 8-11, whereinsaid apparatus measures forces by which the tire acts on the first andsecond planes of the tire while the tire is rotating and thecircumferential surface of said rotating drum is pressed against thetread surface of the tire with a second pressing force, the secondpressing force producing a friction force between said rotating drum andthe tire, the friction force being so large as enough to prevent freerotation of said rotating drum and is smaller than the measurement errorof the forces measured at the first and second positions.
 13. Anapparatus according to claim 12, wherein one of the forces which thetire acts on first and second planes of the tire exceeds a predeterminedvalue when the circumferential surface of said rotating drum is pressedagainst the tread surface of the tire with a first pressing force, thepressing force with which the circumferential surface of a rotating drumis pressed against the tread surface of the tire is changed into thesecond pressing force, and the forces which the tire acts on the firstand second planes of the tire are measured.
 14. An apparatus accordingto any of claims 8-11, further comprising a tire cutting means forcutting the tire so that the amplitude of fluctuation of the force bywhich the tire acts on the first plane and the amplitude of fluctuationof the force by which the tire acts on the second plane are decreased,the forces being measured when said rotating drum is pressed against thetread of the tire with the first pressing force.
 15. An apparatusaccording to claim 12, further comprising a tire cutting means forcutting the tire so that the amplitude of fluctuation of the force bywhich the tire acts on the first plane and the amplitude of fluctuationof the force by which the tire acts on the second plane are decreased,the forces being measured when said rotating drum is pressed against thetread of the tire with the second pressing force.
 16. An apparatusaccording to claim 8-11, further comprising a marking means for markingthe position at which the tire should be cut and the amount by which itshould be cut so that the amplitude of fluctuation of the force by whichthe tire acts on the first plane and the amplitude of fluctuation of theforce by which the tire acts on the second plane will be decreased, theforces being measured when said rotating drum is pressed against thetread of the tire with the first pressing force.
 17. An apparatusaccording to claim 12, further comprising a marking means for markingthe position at which the tire should be cut and the amount by which itshould be cut so that the amplitude of fluctuation of the force by whichthe tire acts on the first plane and the amplitude of fluctuation of theforce by which the tire acts on the second plane will be decreased, theforces being measured when said rotating drum is pressed against thetread of the tire with the second pressing force.